1. Field of the Invention
The present invention relates to a honeycomb filter, an exhaust gas purifying apparatus including the honeycomb filter, and a method for manufacturing the honeycomb filter.
2. Discussion of the Background
In recent years, particulate matter (hereinafter, also referred to as “PM”) such as soot discharged from internal combustion engines of vehicles such as buses and trucks, construction machines and the like has raised serious problems as contaminants harmful to the environment and the human body. For this reason, various honeycomb filters, which use a porous ceramic honeycomb structure, have been proposed as filters that capture PM in exhaust gases and purify the exhaust gases.
As a material for such a honeycomb filter, silicon carbide has been known. In the case where silicon carbide is used as the material for the honeycomb filter, since the silicon carbide has a high coefficient of thermal expansion, a structure of an aggregated honeycomb filter is adopted, in which a plurality of pillar-shaped porous ceramic sintered bodies (honeycomb fired bodies), each having a large number of cells longitudinally placed in parallel with one another, are combined with one another.
As such an aggregated honeycomb filter, JP-A 2001-162121 has disclosed a honeycomb filter including an aggregated body of honeycomb fired bodies (ceramic block) manufactured by combining a plurality of honeycomb fired bodies with one another, cutting a periphery of the ceramic block so as to have a cross-section in an almost circular shape or the like, and forming a smoothing layer on the peripheral face having irregularities thereon exposed by the cutting process.
The smoothing layer is formed by filling irregularities corresponding to the shapes of the cell walls exposed by the cutting process so that the honeycomb filter is formed into a round pillar shape or the like.
The contents of JP-A 2001-162121 are incorporated herein by reference in their entirety.